Understanding the biological mechanisms of the innate "sand-hold" behavior of Hummingbird Bobtail Squid hatchlings
Cephalopods (squids, octopus, cuttlefish) are model organisms for analyzing cognitive function because of their high degree of neural complexity and their unique survival strategies. Hummingbird bobtail squids (Euprymna berryi) have a unique camouflage behavior, in which they hide in the sandy sediments of their habitats by burying and retaining sand on their skin. Various ideas of how these squid retain sediment on their skin have been proposed, including a secreted adhesive or mucus. However, we found that adult E. berryi control the sand on their skin through a serotonin pathway. In adults, erector muscles and long, tentacle-like filaments emerge from the skin, extending between mucus-producing cells and microvilli. Extraordinarily, they can hold sand on their skin and uncloak themselves instantaneously, a strategy we refer to as "sandhold". Although the literature reports bobtails are paralarval upon hatching, we found that E. berryi hatchlings bury and perform "sandhold"; immediately upon hatching, despite being the size of a grain of rice. Hatchlings exhibit a circadian rhythm parallel to adults. Strikingly, there is no published research that analyzes these behaviors and determines whether they hold onto sand using the same mechanisms as adults. We hypothesize that sand type affects the initiation and success of sandhold through a combination of neurological and dermal-muscular processes, forcing the use of other methods of skin camouflage if the grain is too large for the hatchlings to retain. Bobtails were subjected to various sand types during the daylight hours of their circadian rhythm. Videos were recorded using high-resolution magnification equipment (GoPro 11) in a controlled arena. BORIS was used to behavioral score bobtail camouflage behaviors and statistical analysis was conducted using Prism software. Researching the developmental stages of this highly innate behavior will advance our understanding of ecological pressure that shapes the evolution of underlying conserved neural processes.